Fiber optic connector microlens with self-aligning optical fiber cavity

ABSTRACT

A fiber optical connector microlens is provided with a self-aligning optical fiber cavity. The microlens includes a convex first lens surface and a second lens surface. A fiber alignment cavity is integrally formed with the second lens surface to accept an optical fiber core. A lens body is interposed between the first and second lens surfaces, having a cross-sectional area with a lens center axis, and the fiber alignment cavity is aligned with the lens center axis. In a first aspect, the fiber alignment cavity penetrates the lens second surface. In a second aspect, an integrally formed cradle with a cradle surface extends from the lens second surface, and a channel is formed in the cradle surface, with a center axis aligned with the lens center axis. The fiber alignment cavity includes a bridge covering a portion of the channel.

RELATED APPLICATIONS

This application is a Continuation-in-Part of a pending applicationentitled, FIBER OPTIC JACK WITH HIGH INTERFACE MISMATCH TOLERANCE,invented by Igor Zhovnirovsky et al., Ser. No. 12/793,513, filed Jun. 3,2010;

which is a Continuation-in-Part of a pending application entitled, FIBEROPTIC CABLE WITH HIGH INTERFACE MISMATCH TOLERANCE, invented by IgorZhovnirovsky et al., Ser. No. 12/784,849, filed May 21, 2010;

which is a Continuation-in-Part of a pending application entitled,PUNCH-DOWN FIBER OPTIC CABLE TERMINATION, invented by Igor Zhovnirovskyet al., Ser. No. 12/756,087, filed Apr. 7, 2010;

which is a Continuation-in-Part of a pending application entitled,CONNECTOR JACK PROCESSING BACKCAP, invented by Igor Zhovnirovsky et al.,Ser. No. 12/652,705, filed Jan. 5, 2010;

which is a Continuation-in-Part of a pending application entitled,OFF-AXIS MISALIGNMENT COMPENSATING FIBER OPTIC CABLE INTERFACE, inventedby Igor Zhovnirovsky et al., Ser. No. 12/581,799, filed Oct. 19, 2009;

which is a Continuation-in-Part of a pending application entitled, FIBEROPTIC CABLE INTERFACE, invented by Igor Zhovnirovsky et al., Ser. No.12/483,616, filed Jun. 12, 2009. All the above-referenced applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to optical cables and, moreparticularly, to a fiber optical plug connector with a mechanism foraligning the core of an optical fiber with a plug microlens.

2. Description of the Related Art

Conventionally, optical fiber connectors are spring-loaded. The fiberendfaces (optical interfaces) of the two connectors are pressedtogether, resulting in a direct glass to glass or plastic to plastic,contact. The avoidance of glass-to-air or plastic-to-air interfaces iscritical, as an air interface results in higher connector losses.However, the tight tolerances needed to eliminate an air interface makethese connectors relatively expensive to manufacture.

FIG. 1 is a partial cross-sectional view of a Transmission OpticalSubAssembly (TOSA) optical cable plug (prior art). The plug 100 is madefrom a plastic housing 102 with a bored ferrule 106 to secure an opticalfiber 108. The plug 100 also includes a plastic lens 110, manufacturedas a subassembly, integrated into the plug. The lens 110 has a curvedsurface to create a focal plane where the plug mates with a jack 112.The lens permits a low loss air gap to be formed between the plug and aconnecting jack. In addition to the expense of manufacturing a 2-partplug, the plug must be made to relatively tight tolerances, so that thelens focal plane aligns with the jack, which also increases the cost ofthe plug.

FIG. 2 is a partial cross-sectional view of an 8 Position 8 Contact(8P8C) interface (prior art). The ubiquitous 8P8C connector is ahardwired electrical connector used commercially and residentially toconnect personal computers, printers, and routers. The 8P8C is oftenreferred to as RJ45. Although the housing/body can be made as aone-piece plastic molding, the spring-loaded contacts and the necessityof cable crimping add to the complexity of manufacturing the part.Advantageously however, the spring-loaded contacts permit the part to bemade to relatively lax tolerances.

As noted in Wikipedia, plastic optical fiber (POF) is an optical fiberwhich is made out of plastic. Conventionally, poly(methyl methacrylate)(PMMA), a transparent thermoplastic (acrylic) alternative to glass, isthe core material, and fluorinated polymers are the cladding material.Since the late 1990s however, much higher-performance POF based onperfluorinated polymers (mainly polyperfluorobutenylvinylether) hasbegun to appear in the marketplace.

In large-diameter fibers, 96% of the cross section is the core thatallows the transmission of light. Similar to conventional glass fiber,POF transmits light (or data) through the core of the fiber. The coresize of POF is in some cases 100 times larger than glass fiber.

POF has been called the “consumer” optical fiber because the fiber andassociated optical links, connectors, and installation are allinexpensive. The conventional PMMA fibers are commonly used forlow-speed, short-distance (up to 100 meters) applications in digitalhome appliances, home networks, industrial networks (PROFIBUS,PROFINET), and car networks (MOST). The perfluorinated polymer fibersare commonly used for much higher-speed applications such as data centerwiring and building LAN wiring.

For telecommunications, the more difficult to use glass optical fiber ismore common. This fiber has a core made of germania-doped silica.Although the actual cost of glass fibers is lower than plastic fiber,their installed cost is much higher due to the special handling andinstallation techniques required. One of the most exciting developmentsin polymer fibers has been the development of microstructured polymeroptical fibers (mPOF), a type of photonic crystal fiber.

In summary, POF uses PMMA or polystyrene as a fiber core, withrefractive indices of 1.49 & 1.59, respectively. The fiber claddingoverlying the core is made of silicone resin (refractive index ˜1.46). Ahigh refractive index difference is maintained between core andcladding. POF have a high numerical aperture, high mechanicalflexibility, and low cost.

Generally, POF is terminated in cable assembly connectors using a methodthat trims the cables, epoxies the cable into place, and cures theepoxy. ST style connectors, for example, include a strain relief boot,crimp sleeve, and connector (with ferrule). The main body of theconnector is epoxied to the fiber, and fiber is threaded through thecrimp sleeve to provide mechanical support. The strain relief bootprevents to fiber from being bent in too small of a radius. Someconnectors rely upon the connector shape for mechanical support, so acrimp sleeve is not necessary.

First, the strain relief boot and crimp sleeve are slid onto the cable.A jacket stripping tool must be used to remove the end portion of thefiber, exposing an aramid yarn (e.g., Kevlar™) covered buffer orcladding layer. Next, a buffer stripping tool is used to remove asection of the buffer layer, exposing the core. After mixing, a syringeis filled with epoxy. A bead of epoxy is formed at the end of theferrule, and the ferrule back-filled with epoxy. The exposed fiber coreis threaded through the connector ferrule with a rotating motion, tospread the epoxy, until the jacket meets the connector. At this pointthe crimping sleeve is slide onto the connector body and crimped in twoplaces. Then, the strain relief boot can be slide over the crimp sleeve.After the epoxy cures, the core extending through the ferrule ispolished with a lapping film. Then, the core is scribed at the pointwhere it extends from the epoxy bead. The extending core portion is thencleaved from the connector and polished in multiple steps.

As noted in the above-referenced parent applications, the advantages ofusing a microlens in a plug or jack connector include the ability tofocus light on point, such as a photodiode or optical fiber core face,while transceiving light in a collimated beam between connectors.However, the focusing of light on a fiber core face requires that thefiber core and microlens be properly aligned.

It would be advantageous if an optical connector plug had a mechanismfor self-aligning an optical fiber core with a plug microlens.

SUMMARY OF THE INVENTION

According, a fiber optical connector microlens is provided with aself-aligning optical fiber cavity. The microlens includes a convexfirst lens surface and a second lens surface. A fiber alignment cavityis integrally formed with the second lens surface to accept an opticalfiber core. A lens body is interposed between the first and second lenssurfaces, having a cross-sectional area with a lens center axis, and thefiber alignment cavity is aligned with the lens center axis. In a firstaspect, the fiber alignment cavity is formed in (penetrates) the lenssecond surface.

In a second aspect, an integrally formed cradle with a cradle surfaceextends from the lens second surface, and a channel is formed in thecradle surface, with a center axis aligned with the lens center axis.The fiber alignment cavity includes a bridge covering a portion of thechannel. In a related aspect, a crimping plate with an interior surfaceis mechanically secured to the cradle, and a crimping channel formed inthe crimping plate interior surface, with a center axis aligned with thelens center axis. The fiber alignment cavity is formed between thecradle channel and crimping channel.

In yet another aspect, the fiber alignment cavity is an integrallyformed tube extending from the lens second surface, with a center axisaligned with the lens center axis. The tube has a proximal end adjacentthe lens second surface with a first diameter to accept an optical fibercore, and a distal end with a second diameter to accept an optical fiberwith a cladding layer.

Additional details of the above-described microlens with self-aligningoptical fiber cavity, and a fiber optic connector plug with an opticalfiber self-alignment mechanism, are provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a Transmission OpticalSubAssembly (TOSA) optical cable plug (prior art).

FIG. 2 is a partial cross-sectional view of an 8 Position 8 Contact(8P8C) interface (prior art).

FIG. 3 is a diagram depicting a fiber optic cable.

FIGS. 4A and 4B are a more detailed depiction of the first plugmicrolens of FIG. 3.

FIGS. 5A and 5B are partial cross-sectional and plan views,respectively, of the first plug of FIG. 3.

FIG. 6 is a partial cross-sectional view of the first plug microlens ofFIG. 3.

FIGS. 7A and 7B are drawings depicting a fiber optic cable with a cablesection that includes a first plurality of fiber optic lines.

FIG. 8 is a diagram depicting communicating jack and plug microlens.

FIG. 9 is a model calculation graphically depicting the couplingefficiency of the system of FIG. 8.

FIG. 10 is a diagram depicting the fiber core acceptance angle.

FIG. 11 is a graph depicting the relationship between couplingefficiency and fiber lateral decentering (Δ).

FIG. 12 is a diagram depicting the effective focal length of the plugmicrolens.

FIG. 13 is a table of tolerances cross-referenced to fiber lateraldecentering.

FIG. 14 is a graph depicting coupling efficiency as a function ofphotodiode (PD) decentering.

FIG. 15 is a diagram depicting the relationship between fiberdecentering and lens tilt.

FIG. 16 is a diagram depicting the relationship between PD decenteringand lens tilt.

FIG. 17 is a diagram depicting the relationship between PD decenteringand groove (channel) placement error.

FIG. 18 is a diagram depicting the consequences of shortening the focallength of the plug, without a corresponding change in the jack lens.

FIGS. 19A and 19B are partial cross-sectional views depicting a firstvariation of a fiber optical connector microlens with a self-aligningoptical fiber cavity.

FIGS. 20A, 20B, and 20D are partial cross-sectional views depicting asecond variation of the fiber optical connector microlens withself-aligning optical fiber cavity, and FIGS. 20C and 20E areperspective drawings.

FIGS. 21A through 21C are partial cross-sectional views depicting athird variation of the fiber optical connector microlens withself-aligning optical fiber cavity.

FIGS. 22A and 22B are partial cross-sectional views depicting a fourthvariation of the fiber optical connector microlens with self-aligningoptical fiber cavity.

FIGS. 23A through 23C are partial cross-sectional views depicting afirst variation of a fiber optic connector plug with an optical fiberself-alignment mechanism.

FIGS. 24A and 24B are partial cross-sectional views depicting a secondvariation of a fiber optic connector plug with an optical fiberself-alignment mechanism.

FIGS. 25A and 25B are partial cross-sectional views depicting a thirdvariation of a fiber optic connector plug with an optical fiberself-alignment mechanism.

FIGS. 26A through 26C are partial cross-sectional views depicting afourth variation of a fiber optic connector plug with an optical fiberself-alignment mechanism.

DETAILED DESCRIPTION

FIG. 3 is a diagram depicting a fiber optic cable. The fiber optic cable300 comprises a cable section 302 including at least one length of fiberoptic line or core 304 having a first end 306 and a second end 308. Afirst plug 310 includes a mechanical body 312 shaped to selectivelyengage and disengage a first jack housing 314 (shown in phantom), and amicrolens 316. As defined herein, the plug is mechanically engaged withthe jack when the plug is fully inserted into the jack. In some aspects,a locking mechanism is enabled when the plug and jack are mechanicallyengaged. An RJ-45 connector is one example of such a locking typemechanical engagement (as shown). In other aspects, mechanicalengagement is obtained with a pressure or friction type fit. A universalserial bus (USB) connector, microUSB, HDMI, and DisplayPort are someexamples of a pressure/friction type of mechanical engagement.Alternately stated, a plug and jack are mechanically engaged when theyare mated sufficiently to perform their intended electrical or opticalfunctions.

The first plug microlens 316 has a planar surface 318 to engage thefiber optic line first end 306 and a convex surface 320 to transceivelight in a first collimated beam 322 with a first jack optical interface324. Likewise, a second plug 326 includes a mechanical body 328 shapedto selectively engage and disengage a second jack housing 330 (shown inphantom), and a microlens 332. The second plug microlens 332 has aplanar surface 334 to engage the fiber optic line second end 308 and aconvex surface 336 to transceive light in a second collimated beam 338with a second jack optical interface 340.

A collimated beam is light whose rays are parallel, and therefore thebeam spreads slowly as it propagates. Laser light from gas or crystallasers is naturally collimated because it is formed in an optical cavitybetween two mirrors, in addition to being coherent. However, diodelasers do not naturally emit collimated light, and therefore collimationinto a beam requires a collimating lens. A perfect parabolic mirror willbring parallel rays to a focus at a single point. Conversely, a pointsource at the focus of a parabolic mirror will produce a beam ofcollimated light. Spherical mirrors are easier to make than parabolicmirrors and they are often used to produce approximately collimatedlight. Many types of lenses can also produce collimated light frompoint-like sources.

The fiber optic cable first end 306 is formed in a focal plane 342 ofthe first plug microlens 316, and the fiber optic cable second end 308is formed in a focal plane 344 of the second plug microlens 332. In oneaspect, the first and second plug microlenses 316/332 are made from apolycarbonate resin thermoplastic such as lexan or ultem, and haverespective focal lengths 342 and 344 in the range of 2 to 4 mm. Thefirst and second plug microlens 316 and 332 transceive the collimatedbeams with a beam diameter 346 in the range of 1.2 to 1.3 mm.

As used herein, a jack is the “female” connector and a plug is a mating“male” connector. Note, a portion of the first plug body has been cutaway to show the fiber line 304. In some aspects, a crimping plate isconnected to a cradle portion of the body, to hold the fiber line inplace. See parent application Ser. No. 12/581,799 for additionaldetails.

FIGS. 4A and 4B are a more detailed depiction of the first plugmicrolens of FIG. 3. For clarity, only the microlens 316 is shown. Thefirst plug microlens 316 has a lens center axis 400. As shown in FIG.4B, there is a lens axis tolerance defined by a cone angle 402 of up to0.5 degrees (+/−0.5 degrees from a perfectly aligned, or tolerancemidpoint lens center axis) as a result of the first plug mechanical bodytolerances, when engaging the first jack mechanical body. That is, dueto “play” between the jack and plug housings, resulting from design andmanufacturing tolerances, the lens axis may be misaligned as much as 0.5degrees. Note: although misalignment is only shown in an XY plane, thelens axis tolerance may define a circular cone with respect to aperfectly aligned center axis.

The first plug microlens has a diameter 404 in the range of 2 to 3 mm,and the first collimated beam diameter (see FIG. 3, reference designator346) is transceived within the microlens diameter 404. The first plugmicrolens 316 includes a cylindrical section 406 interposed between theplanar surface 318 and the convex surface 320.

In one aspect, the first plug microlens cylindrical section 406 has alength 408 in the range of 4 to 6 mm and the convex surface 320 has aradius of curvature in the range of 1.5 to 2.5 mm. The second plugmicrolens, not shown, has the same lens dimensions and tolerances as thefirst plug microlens.

FIGS. 5A and 5B are partial cross-sectional and plan views,respectively, of the first plug of FIG. 3. A first plug cradle 500 has achannel or groove 502 to accept the fiber optic line first end 306 (notshown in FIG. 5A). The channel 502 has a center axis 504 with atolerance 506 of up to 30 microns with respect to the lens center axis400. Alternately stated, the center axis of the fiber line core may havea tolerance of up to 30 microns with respect to the lens center axis.The first plug includes a gap 508 between the microlens planar surface318 and the first fiber optic cable first end of up to 0.4 mm. Thesecond plug (not shown) likewise has a cradle, channel, dimensions, andtolerance as described above.

FIG. 6 is a partial cross-sectional view of the first plug microlens ofFIG. 3. The first plug microlens modifies the magnification of lightbetween the collimated beam 322 at convex surface 320 and a point 600 onthe planar surface 318 along the lens center axis 400, forming a conewith an angle 602 of 10 to 11 degrees with respect the lens center axis400. The second plug (not shown) likewise has the samemagnification/demagnification features as the first plug microlens.

FIGS. 7A and 7B are drawings depicting a fiber optic cable with a cablesection that includes a first plurality of fiber optic lines. In FIG.7A, lines 304 a through 304 d are shown. Each fiber optic line 304 has afirst end 306 and a second end 308. In the example of FIG. 7A, the firstplurality is equal to four, but the cable section 302 is not limited toany particular number of lines. The first and second plugs 310/326include the first plurality of microlenses, respectively 316 a-316 d and332 a-332 d. Each microlens 316/332 has a planar surface 318/334 toengage a corresponding fiber optic line end and a convex surface 320/336to transceive light in a corresponding collimated beam with a jackoptical interface (not shown). Each fiber optic cable end 306/308 isformed in a focal plane 342/344 of a corresponding first plug microlens316/332. A layer of cladding 700 is also shown surrounding the fibercores 304. In one aspect the cladding diameter is about 0.49 mm and thecore diameter is about 0.0625 mm. Typically, the cladding is coveredwith a buffer and plenum jacket, which is not shown because it isstripped away.

As shown in FIG. 7B, there may be multiple rows of microlenses, e.g., atop row and a bottom row. Note: a completely assembled plug wouldinclude top and bottom crimping plates (not shown), to secure the fiberlines 304 to the cradle 500. In one aspect, the first plug mechanicalbody has the form factor of an 8 Position 8 Contact (8P8C) plugmechanical body.

FIGS. 19A and 19B are partial cross-sectional views depicting a firstvariation of a fiber optical connector microlens with a self-aligningoptical fiber cavity. The microlens 1900 comprises a convex first lenssurface 1902 and a second lens surface 1904. Although the second lenssurface 1904 is shown as planar, in other aspects it may also be convex(see FIG. 20A). Further, in other aspects the second lens surface can beaspheric or holographic. As is well known in the art, a convex lenssurface can be described by a portion of a circular circumference. Thatis, a convex surface be can defined by a radius with respect to a centerpoint. An aspheric or aspherical lens is a more complicated shape thatmay include a surface portion defined by a radius, and other portionsdefined by a hyperbola or parabola, for example. A holographic lensmight be fabricated from a plurality of closely packed, distinct convex(or aspheric) lens. For example, a holographic lens might be a fly's-eyeor integral lens array.

A fiber alignment cavity 1906 is integrally formed with the second lenssurface 1904 to accept an optical fiber core 1908. In this aspect, thefiber alignment cavity 1906 is formed in the lens second surface 1904.That is, the fiber alignment cavity penetrates the lens second surface1904.

A lens body 1910 is interposed between the first lens surface 1902 andsecond lens surface 1904. The lens body 1910 has a lens body length1912, and a cross-sectional area 1914 with a lens center axis 1916. Inone aspect, the fiber alignment cavity 1906 has a center axis 1928aligned with the lens center axis 1916. Typically, the fiber alignmentcavity 1906 has a length 1918, aligned with the lens center axis 1916,which is in the range of 5 to 10% of the lens body length 1912. In oneaspect, a focal point 1924 is formed inside the fiber alignment cavity1906, when transceiving light in a collimated beam 1926 via the firstlens surface 1902. Note, when the second lens surface 1904 is planar, itcan be said that the focal point is formed as a result of the first lenssurface, as the planar surface does not modify magnification. When thesecond lens surface is convex, the focal point is ultimately formed as aresult of the second (convex) lens surface. Alternately stated, thefocal point is formed in the focal plane of the first lens surface, asmodified by the second lens surface. The effect of such a microlens withtwo convex lens surfaces can be seen in FIGS. 15-17, in the transceivingof light between a jack lens and an optical element (VCSEL orphotodiode).

The first and second lens surfaces 1902/1904 may be formed from apolycarbonate resin thermoplastic such as lexan or ultem. The fiberalignment cavity 1906 has a minimal cross-section 1920 with a shape suchas a triangle, a square, a rectangle, circle, or an oval (a circle isshown). Typically, the fiber alignment cavity 1906 accepts an opticalfiber core 1908 having a first diameter 1922, and the cavity minimalcross-section 1920 is about 5% greater than the first diameter 1922.Note: these same dimensional features also apply to the other aspects ofthe fiber alignment cavity presented below.

FIGS. 20A, 20B, and 20D are partial cross-sectional views depicting asecond variation of the fiber optical connector microlens withself-aligning optical fiber cavity, and FIGS. 20C and 20E areperspective drawings. An integrally formed cradle 2000 with a cradlesurface 2002 extends from the lens second surface 1906. A channel 2004is formed in the cradle surface 2002, with a center axis 2006 alignedwith the lens center axis 1916. The fiber alignment cavity 1906 includesa bridge 2008 covering a portion of the channel 2004. As shown in FIGS.20A and 20B, the bridge 2008 includes a first end 2010 connected to thesecond lens surface 1904, and an exposed second end 2012. FIG. 20C is aperspective drawing illustrating the variation of FIGS. 20A and 20B. Asshown in FIG. 20D, the bridge 2008 includes an exposed first end 2010separated from the second lens surface 1904 by an opening 2014, and anexposed second end 2012. FIG. 20E is a perspective drawing illustratingthe variation of FIGS. 20 D.

FIGS. 21A through 21C are partial cross-sectional views depicting athird variation of the fiber optical connector microlens withself-aligning optical fiber cavity. In this aspect, the fiber alignmentcavity 1906 includes an integrally formed tube 2100 extending from thelens second surface 1904, with a center axis aligned 2102 with the lenscenter axis 1916. As shown in FIG. 21A, the tube 2100 has a proximal end2104 adjacent the lens second surface 1906 with a first diameter 2106 toaccept an optical fiber core 1908, and a distal end 2108 with a seconddiameter 2110 to accept an optical fiber with a cladding layer 2112.

FIGS. 22A and 22B are partial cross-sectional views depicting a fourthvariation of the fiber optical connector microlens with self-aligningoptical fiber cavity. An integrally formed cradle 2000 with a cradlesurface 2002 extends from the lens second surface 1904. A cradle channel2004 is formed in the cradle surface 2002, with a center axis 2006aligned with the lens center axis 1916. A crimping plate 2200 with aninterior surface 2202 is mechanically secured to the cradle 2000. Anumber of means are known in the art to permanently or selectivelysecure the crimping late 2200 to the cradle 2000. The microlensalignment mechanism is not limited to any particular mechanism. In someaspects, the crimping plate 2200 is used to compress the fiber coreand/or fiber cladding layer, to hold the fiber in place with respect tothe microlens and cradle.

As shown, a crimping channel 2204 is formed in the crimping plateinterior surface 2202, with a center axis 2206 aligned with the lenscenter axis 1916 (and channel center axis 2006). The fiber alignmentcavity 1906 is formed between the cradle channel 2006 and crimpingchannel 2204. In another aspect not shown, the cradle and crimpingchannels have a first diameter to accommodate the fiber core and asecond diameter to accommodate a fiber cladding layer.

FIGS. 23A through 23C are partial cross-sectional views depicting afirst variation of a fiber optic connector plug with an optical fiberself-alignment mechanism. The plug 2300 comprises a mechanical body 2302shaped to selectively engage and disengage a jack housing 2304 (shown inphantom), and a microlens 1900. As described above in the explanation ofFIGS. 19 through 22B, the microlens 1900 has a convex first lens surface1902 to transceive light in a collimated beam 2306 with a jack opticalinterface 2308, and a second lens (convex or planar) surface 1904. Afiber alignment cavity 1906 is integrally formed with the second lenssurface 1904 to accept an optical fiber core. Typically, the mechanicalbody 2302 and microlens 1900 are a single injection molded piece madefrom a polycarbonate resin thermoplastic such as lexan or ultem. As inFIGS. 19A and 19B, the fiber alignment cavity 1906 penetrates the lenssecond surface 1904. As above, the microlens 1900 forms a focal point1924 inside the fiber alignment cavity 1906, when transceiving light ina collimated beam 2306 via the first lens surface 1902.

FIG. 23B depicts a plug with a first plurality of microlenses, 1900 athrough 1900 n, where n is a variable not limited to any particularvalue. Each microlens 1900 has a convex first surface 1902 to transceivelight in a corresponding collimated beam 2306 with a first jack opticalinterface (not shown), the second lens surface 1904, and the fiberalignment cavity 1906 variation depicted in FIG. 23A. FIG. 23C isanother partial cross-sectional view. Shown are m rows of microlenses1900, where m is not limited to any particular value.

FIGS. 24A and 24B are partial cross-sectional views depicting a secondvariation of a fiber optic connector plug with an optical fiberself-alignment mechanism. As in FIGS. 20A through 20D, a lens body 1910is interposed between the first and second lens surfaces 1902/1904,having a cross-sectional area with a lens center axis 1916. A cradle2000 is integrally formed with the mechanical housing 2302 and microlens1900, with a cradle surface 2002 extending from the lens second surface1904. A channel 2004 is formed in the cradle surface 2002, with a centeraxis 2006 aligned with the lens center axis 1916. The fiber alignmentcavity 1906 includes a bridge 2008 covering a portion of the channel2004, with a first end 2010 connected to the second lens surface 1904,and an exposed second end 2012. In another aspect not shown here (seeFIG. 20D), there is an opening between the bridge first end 2010 and thelens second surface 1904.

FIG. 24B depicts a plug with a first plurality of microlenses, 1900 athrough 1900 n, where n is a variable not limited to any particularvalue. Each microlens 1900 has a convex first surface 1902 to transceivelight in a corresponding collimated beam 2306 with a first jack opticalinterface (not shown), the second lens surface 1904, and the fiberalignment cavity 1906 variation depicted in FIG. 24A. Although notexplicitly shown, the plug may comprise m rows of microlenses, where mis not limited to any particular value.

FIGS. 25A and 25B are partial cross-sectional views depicting a thirdvariation of a fiber optic connector plug with an optical fiberself-alignment mechanism. As in FIGS. 21A and 21B, a lens body 1901 isinterposed between the first and second lens surfaces 1902/1904, havinga cross-sectional area with a lens center axis 1916. The fiber alignmentcavity 1906 includes a tube 2100, integrally formed with the mechanicalbody 2302 and microlens 1900, extending from the lens second surface1904, with a center axis 2102 aligned with the lens center axis 1916.Although only a constant diameter variation is explicitly depicted here,the tube may have a second diameter to accept a fiber cladding layer asshown in FIG. 21B

FIG. 25B depicts a plug with a first plurality of microlenses, 1900 athrough 1900 n, where n is a variable not limited to any particularvalue. Each microlens 1900 has a convex first surface 1902 to transceivelight in a corresponding collimated beam 2306 with a first jack opticalinterface (not shown), the second lens surface 1904, and a fiberalignment cavity 1906 variation depicted in FIG. 25A. Although notexplicitly shown, the plug may comprise m rows of microlenses, where mis not limited to any particular value.

FIGS. 26A through 26C are partial cross-sectional views depicting afourth variation of a fiber optic connector plug with an optical fiberself-alignment mechanism. As in FIGS. 22A and 22B, a lens body 1910 isinterposed between the first and second lens surfaces 1902/1904, havinga cross-sectional area with a lens center axis 1916. A cradle 2000 isintegrally formed with the mechanical body 2302 and microlens 1900, witha cradle surface 2002 extending from the lens second surface 1904. Acradle channel 2004 is formed in the cradle surface 2002, with a centeraxis 2006 aligned with the lens center axis 1916. A crimping plate 2200with an interior surface 2202 is mechanically secured to the cradle2000. A crimping channel 2204 is formed in the crimping plate interiorsurface 2202, with a center axis 2206 aligned with the lens center axis1916 and cradle channel 2004. The fiber alignment cavity 1906 is formedbetween the cradle channel 2004 and crimping channel 2204.

FIGS. 26B and 26C depicts a plug with a first plurality of microlenses,1900 a through 1900 n, where n is a variable not limited to anyparticular value. Each microlens 1900 has a convex first surface 1902 totransceive light in a corresponding collimated beam 2306 with a firstjack optical interface (not shown), the second lens surface 1904, andthe fiber alignment cavity 1906 variation depicted in FIG. 26A. Althoughnot explicitly shown, the plug may comprise m rows of microlenses, wherem is not limited to any particular value. Note: only the cradle channel2004 can be seen in FIG. 26B.

FIG. 8 is a diagram depicting communicating jack and plug microlens. Atransmitting vertical-cavity surface-emitting laser (VCSEL) 800 has anumerical aperture (NA) of 0.259, so that light is emitted into a 30degree cone at the 1/e² point:NA=1 sin 15°=0.259.

The NA of the fiber line 304 is 0.185, which translates into anacceptance angle cone of about 21 degrees.

One aspect of coupling efficiency is reflection (R). A normally incidentreflection of ˜4.9% is typical of each air/lexan interface. For rays notnormally incident, R is a function of angle of incidence andpolarization:

n for lexan @ 850 nm˜1.568;

n′ for air=1;R=((n−n′)/(n+n′))2˜4.9%;

Assuming each jack and plug use a microlens, there are 3 air-to-lexaninterfaces. The fiber/plug interface is filled with index-matchingfluid, so no reflection is assumed for this interface;(1−0.049)³=86% optimal coupling efficiency.

FIG. 9 is a model calculation graphically depicting the couplingefficiency of the system of FIG. 8. The model shows that 86% of thetransmitted light falls within a circle of about 0.07 mm, which is aboutthe diameter of a particular POF optical fiber core.

FIG. 10 is a diagram depicting the fiber core acceptance angle. Assuminga 70 micron diameter gradient index (GRIN) fiber core, the NA is 0.185,which translates to an acceptance angle of +/−10.7°. This assumptionignores the fact that the acceptance angle falls of towards to coreedges.

Many of the system tolerances can be converted into an effective fiberlateral decenter. For example, VCSEL lateral decentering can bemultiplied by the system magnification. Plug tilt can be accounted forby taking the taking the tangent of the tilt and multiplying it by theeffective focal length of the plug lens. Most of the other tolerancestend to change the shape of the beam rather than causing the beam to“walk off” the face of the fiber end. With respect to the fiber line ofFIG. 10, “lateral” refers to the X plane (in and out of the page) and Yplane (from the page top to the page bottom). The Z plane would be leftto right on the page.

FIG. 11 is a graph depicting the relationship between couplingefficiency and fiber lateral decentering (Δ). The relationship isnonlinear, steeply degrading at about 30 microns of decentering, orabout half the core diameter.

FIG. 12 is a diagram depicting the effective focal length of the plugmicrolens. Assuming a radius of curvature of 1.971 mm, an overall lenslength of 5.447 mm, and a lexan material, the effective focal length ofthe plug is:

eflplug˜5.447 mm/n_(lexan);

eflplug=3.471 mm.

FIG. 13 is a table of tolerances cross-referenced to fiber lateraldecentering.

The following is an equation for worst-case effective fiber decenteringusing tolerances T1 through T5 from the Table of FIG. 13:

$\begin{matrix}{{{{effective}\mspace{14mu}{fiber}\mspace{14mu}{decenter}} = {{T\; 1(1.36)} + {T\; 2(1.36)} + {3.471{\tan\left( {T\; 3} \right)}} + {T\; 4} + {T\; 5}}};} \\{= {{1.36\left( {{T\; 1} + {T\; 2}} \right)} + {3.471\left\lbrack {\tan\left( {T\; 3} \right)} \right\rbrack} + {T\; 4} + {T\; 5}}} \\{\sim {{1.36\left( {{T\; 1} + {T\; 2}} \right)} + {3.471\left( {T\; 3} \right)} + {T\; 4} + {T\; 5}}}\end{matrix}$

The tolerances T1 and T2 are proportional to the system magnification(1.36), and the lens tilt is expressed as a tangent in radians, assuminga small-angle approximation. Note: T2 circuit misalignment refers to therelationship between the circuit board on which the optical elements(VCSEL and PD) are mounted and the microlens. T1 VCSEL/PD misalignmentrefers to misalignment between the VCSEL/PD and the circuit board. TheT4 and T5 tolerances are outside the system magnification, and need notbe system normalized.

In matrix form the equation is:

$\begin{bmatrix}{T\; 1} & {T\; 2} & {T\; 3} & {T\; 4} & {T\; 5}\end{bmatrix}\begin{bmatrix}1.36 \\1.36 \\3.471 \\1 \\1\end{bmatrix}$

where

-   -   1.36=current system magnification;    -   3.471 mm=plug focal length; and,    -   Ti=ith tolerance.

FIG. 14 is a graph depicting coupling efficiency as a function ofphotodiode (PD) decentering.

FIG. 15 is a diagram depicting the relationship between fiberdecentering and lens tilt:

$\begin{matrix}{\Delta = {{effective}\mspace{14mu}{fiber}\mspace{14mu}{decenter}}} \\{{= {{fplug}*\tan\mspace{11mu}\theta}};} \\{{= {3.471\mspace{14mu}{mm}*\tan\mspace{11mu}\theta}};}\end{matrix}$

If θ=0.5°, then Δ=30.3 μm. Note: the angle θ has been exaggerated.

FIG. 16 is a diagram depicting the relationship between PD decenteringand lens tilt.

$\begin{matrix}{\Delta = {{effective}\mspace{14mu}{PD}\mspace{14mu}{decenter}}} \\{{= {{fjack}*\tan\mspace{11mu}\theta}};} \\{{= {2.504\mspace{14mu}{mm}*\tan\mspace{11mu}\theta}};}\end{matrix}$

If θ=0.5°, then Δ=21.9 μm.

FIG. 17 is a diagram depicting the relationship between PD decenteringand groove (channel) placement error. The channel placement error mayalso be understood as a lens placement error relative to the channel.The effective PD decenter=channel placement error*Msys;

where Msys is the system magnification (0.727=1/1.36).

A channel placement error of 7.1 μm results in effective PD decenteringof 7.1 μm*0.727=5.2 μm in both the X and Y planes. The overalldecentering (the hypotenuse of the triangle) is:sqrt(5²+5²)=7.1 microns.

A placement error of 10 microns results in a PD decentering of about 10microns.

FIG. 18 is a diagram depicting the consequences of shortening the focallength of the plug, without a corresponding change in the jack lens. Ifthe plug focal length (fplug) is decreased, the loss in couplingefficiency due to plug angular misalignment can be reduced. However, thefiber core would be overfilled (exceeding the NA 0.185), which wouldresult in some lost energy.

A fiber optic plug and microlens fiber alignment mechanism have beenprovided. Some examples of particular housing designs, tolerances, anddimensions have been given to illustrate the invention. However, theinvention is not limited to merely these examples. Other variations andembodiments of the invention will occur to those skilled in the art.

1. A fiber optical connector microlens with a self-aligning opticalfiber cavity, the microlens comprising: a convex first lens surface; asecond lens surface; and, a fiber alignment cavity integrally formedwith the second lens surface, the fiber alignment cavity having aproximal end adjacent the lens second surface with a first diameter toaccept an unclad optical fiber core without a ferrule, and a distal endwith a second diameter to accept an optical fiber cladding layer.
 2. Themicrolens of claim 1 wherein the second lens surface is selected from agroup consisting of convex, aspheric, holographic, and planar surfaces.3. The microlens of claim 1 further comprising: a lens body interposedbetween the first and second lens surfaces, having a cross-sectionalarea with a lens center axis; and, wherein the fiber alignment cavityhas a center axis aligned with the lens center axis.
 4. The microlens ofclaim 1 wherein the fiber alignment cavity penetrates the lens secondsurface.
 5. The microlens of claim 4 further comprising: a lens bodyinterposed between the first and second lens surfaces, having a lensbody length, and a cross-sectional area with a lens center axis; and,wherein the fiber alignment cavity has a length with a center axis,aligned with the lens center axis, that is in a range of 5 to 10% of thelens body length.
 6. The microlens of claim 1 wherein the fiberalignment cavity has a minimal cross-section with a shape selected froma group consisting of a triangle, a square, a rectangle, circle, and anoval.
 7. The microlens of claim 6 wherein the fiber alignment cavityaccepts an optical fiber core having a first diameter, and the cavityminimal cross-section area is about 5% greater than the first diameter.8. The microlens of claim 1 wherein a focal point is formed inside thefiber alignment cavity, when transceiving light in a collimated beam viathe first lens surface.
 9. The microlens of claim 1 wherein the firstand second lens surfaces are formed from a polycarbonate resinthermoplastic selected from a group consisting of lexan and ultem. 10.The microlens of claim 1 further comprising: a lens body interposedbetween the first and second lens surfaces, having a cross-sectionalarea with a lens center axis; an integrally formed cradle with a cradlesurface extending from the lens second surface; a channel formed in thecradle surface, with a center axis aligned with the lens center axis;and, wherein the fiber alignment cavity includes a bridge covering aportion of the channel.
 11. The microlens of claim 10 wherein the bridgeincludes a first end connected to the second lens surface, and anexposed second end.
 12. The microlens of claim 10 wherein the bridgeincludes an exposed first end separated from the second lens surface byan opening, and an exposed second end.
 13. The microlens of claim 1further comprising: a lens body interposed between the first and secondlens surfaces, having a cross-sectional area with a lens center axis;and, wherein the fiber alignment cavity includes an integrally formedtube extending from the lens second surface, with a center axis alignedwith the lens center axis.
 14. The microlens of claim 13 wherein thetube has a proximal end adjacent the lens second surface with a firstdiameter to accept the unclad optical fiber core, and a distal end witha second diameter to accept the optical fiber cladding layer.
 15. Themicrolens of claim 1 further comprising: a lens body interposed betweenthe first and second lens surfaces, having a cross-sectional area with alens center axis; an integrally formed cradle with a cradle surfaceextending from the lens second surface; a cradle channel formed in thecradle surface, with a center axis aligned with the lens center axis;and, a crimping plate with an interior surface, mechanically secured tothe cradle; a crimping channel formed in the crimping plate interiorsurface, with a center axis aligned with the lens center axis; and,wherein the fiber alignment cavity is formed between the cradle channeland crimping channel.
 16. A fiber optic connector plug with an opticalfiber self-alignment mechanism, the plug comprising: a mechanical bodyshaped to selectively engage and disengage a jack housing, and amicrolens, the microlens having a convex first lens surface totransceive light in a collimated beam with a jack optical interface, asecond lens surface, and a fiber alignment cavity integrally formed withthe second lens surface, fiber alignment cavity having a proximal endadjacent the lens second surface with a first diameter to accept anunclad optical fiber core without a ferrule, and a distal end with asecond diameter to accept an optical fiber cladding layer.
 17. The plugof claim 16 further comprising a plurality of microlenses, each firstplug microlens having a convex first surface to transceive light in acorresponding collimated beam with a first jack optical interface, asecond lens surface, and a fiber alignment cavity integrally formed witheach second lens surface to accept a corresponding unclad optical fibercore.
 18. The plug of claim 16 wherein the mechanical body and microlensare a single injection molded piece made from a polycarbonate resinthermoplastic selected from a group consisting of lexan and ultem. 19.The plug of claim 16 wherein the fiber alignment cavity penetrates thelens second surface.
 20. The plug of claim 16 wherein the microlensforms a focal point inside the fiber alignment cavity, when transceivinglight in a collimated beam via the first lens surface.
 21. The plug ofclaim 16 further comprising: a lens body interposed between the firstand second lens surfaces, having a cross-sectional area with a lenscenter axis; a cradle, integrally formed with the mechanical body andmicrolens, with a cradle surface extending from the lens second surface;a cradle channel formed in the cradle surface, with a center axisaligned with the lens center axis; and, a crimping plate with aninterior surface, mechanically secured to the cradle; a crimping channelformed in the crimping plate interior surface, with a center axisaligned with the lens center axis; and, wherein the fiber alignmentcavity is formed between the cradle channel and crimping channel. 22.The plug of claim 16 further comprising: a lens body interposed betweenthe first and second lens surfaces, having a cross-sectional area with alens center axis; a cradle, integrally formed with the mechanicalhousing and microlens, with a cradle surface extending from the lenssecond surface; a channel formed in the cradle surface, a center axisaligned with the lens center axis; and, wherein the fiber alignmentcavity includes a bridge covering a portion of the channel, with a firstend connected to the second lens surface, and an exposed second end. 23.The plug of claim 16 further comprising: a lens body interposed betweenthe first and second lens surfaces, having a cross-sectional area with alens center axis; and, wherein the fiber alignment cavity includes atube, integrally formed with the mechanical body and microlens,extending from the lens second surface, with a center axis aligned withthe lens center axis.
 24. The microlens of claim 1 further comprising: afiber core interface in the fiber alignment channel adjacent the secondlens surface to accept an index matching fluid.
 25. The plug of claim 16further comprising: a fiber core interface in the fiber alignmentchannel adjacent the second lens surface to accept an index matchingfluid.